Stopwatch Calculator

test.py

"""
A stopwatch records lap times as strings of the form "MM:SS:HS"
  MM = minutes; SS = seconds; and HS = hundredths of a second.  

Write a function that accepts two lap times and calculates their average, 
returning the result in the same string format. 

  Input: "00:02:20" and "00:04:40"
  Output: "00:03:30"

Your answer will be evaluated based on: 
* Working correctly for all possible input stopwatch times 
* The clarity and simplicity of the solution 
* The time taken - we would expect this task to take no more than 15-30 minutes

"""

import time
import datetime
import unittest
 
def split_to_delta(value):
    # timedelta doesn't support strf*
    mins, secs, msecs = value.split(":", 2)
    return datetime.timedelta(minutes=int(mins), seconds=int(secs), 
        milliseconds=int(msecs)*10)
 
def calc_result(value1, value2):
    t1 = split_to_delta(value1)
    t2 = split_to_delta(value2)
 
    total_secs = [ x.total_seconds() for x in (t1, t2)]
 
    # mean average
    avg_secs = (sum(total_secs) / len(total_secs))
 
    # annoyingly, timedelta doesn't have support for any of this
    minutes, seconds = divmod(avg_secs, 60)
    seconds, msecs = divmod(seconds, 1)
    msecs = round(msecs * 100)
 
    return "%02d:%02d:%02d" % ( minutes, seconds, msecs, )
 
class TestStopwatch(unittest.TestCase):
    def test_values(self):
        # test seconds
        result = calc_result("00:02:20", "00:04:40")
        self.assertEquals(result, "00:03:30")
 
        # test minutes
        result = calc_result("02:00:20", "02:50:20")
        self.assertEquals(result, "02:25:20")
 
        # test microseconds partials
        result = calc_result("00:00:01", "00:00:02")
        self.assertEquals(result, "00:00:02")
 
        # test microseconds
        result = calc_result("00:00:01", "00:00:03")
        self.assertEquals(result, "00:00:02")
 
        # test microseconds 10ths
        result = calc_result("00:00:20", "00:00:30")
        self.assertEquals(result, "00:00:25")
 
        # test hours
        result = calc_result("69:00:20", "70:00:30")
        self.assertEquals(result, "69:30:25")
 
        # test days
        result = calc_result("1000:00:20", "1050:00:30")
        self.assertEquals(result, "1025:00:25")
 
if __name__ == '__main__':
    unittest.main()